I just pulled a muscle in my quadricep doing squats and I have a few questions about what happened.

I have been doing 5 sets of 5 reps for squats with about 345 lbs but this past Monday the program I am on required 4 sets of 15 reps. I used 225 lb. I haven't been happy with how low/deep I have been able to squat with heavy weights so I concentrated on going as low as I could. On the 8th rep of the 3rd set I was distracted by someone suddenly standing right behind me checking me out. I think I went all the way down so my butt was on my calves. In any case when I started back up I actually heard as well as felt something go in my outside right quad.

My question, is there a point where one goes too low while squatting that puts the muscle in to some kind of mechanical disadvantage, where you're actually using your strength to pull the muscle apart. It sure felt like it. I had used the hack squat machine with very light weight to warm up. If anyone has any observations or suggestions I would appreciate it.

As it happened it's not too serious, kind of like a charley horse now, but I am taking a week off to heal up. I have been going pretty steady for months so I'm due but I wanted to decide when, not have it decided for me.